Justice Harry Blackmun, the U.S. Supreme Court's senior Justice and the author of the landmark 1973 Roe v. Wade decision, announced his intention to step down. During his 24 years on the high bench, the 85-year-old Justice -- chosen by Richard Nixon in 1970 -- underwent a highly public evolution from conservative to liberal jurist, becoming one of the court's most passionate defenders of constitutional liberties for ordinary citizens. Retiring Senate majority leader George Mitchell was reported to be near the top of the Clinton list of possible replacements.